This invention relates to a method for controlling plasma surface-treatments, specifically a method for controlling plasma surface-treatments which can perform a plurality of kinds of surface treatments on an object to be treated in continuous steps.
Some LSI fabrication processes include surface treatments of thin films with plasma. For example, the ashing of organic thin films is widely used in resist removing steps, and etching with plasma is an essential technique to the etching of micronized patterns of integrated circuits in objects to be treated.
The ashing speed and the etching speed vary depending on various factors, such as resist materials, etched materials, specimen temperatures, processing conditions and other conditions. The ashing requires no precise time control but essentially requires endpoint detection of an ashing because excessive exposure of specimens to plasma causes radiation damages, contamination, etc. The etching requires endpoint detection of an etching because unnecessary parts of oxide films are removed to expose underlying doped layers.
Conventionally an endpoint of an ashing is detected by the method in which an intensity of interference waves of reflected light against a photoresist, and reflected light against the surface of the substrate is measured based on that the intensity of the interference waves correspond to a film thickness of a resist. In addition, for example, as described in Japanese Patent Laid-Open Publication No. 115536/1981, since an emission spectrum abruptly changes at the endpoint of an etching, the change is detected. Fluorescence is detected. Plasma is directly visually observed. Japanese Patent Laid-Open Publication No. 165327/1981 describes a method of detecting a gas pressure in a reaction vessel. On the other hand, in such surface treatments states of surfaces being treated have to be monitored. To this end, surfaces which have been actually treated are checked based on their states, or surfaces being treated are monitored through the above-mentioned optical methods or the visual observation of plasma.
These conventional methods for optically monitoring plasma disadvantageously require spectroscopes and optical instruments, and devices for conducting these methods are accordingly complicated and expensive. In addition, these devices need complicated operations.
Especially in such optical endpoint detection of such surface treatment, monochromators are used. But detected wavelengths vary depending on kinds of films to be surface-treated, e.g., Poly-Si, SiN, etc., and different monochromators have to be needed for respective wavelengths. When a large number of objects are surface-treated, the endpoint detection of the surface treatments are more difficult.
Disadvantageously the visual observation needs some experience, and the human sense is not reliable. In addition, during the visual observation, an operator has to confine himself on the work, which lowers productivities. The method in which states of actually surface-treated objects are checked wastes might waste the objects. The method in which a gas pressure in a reaction vessel is detected must have a vacuum gauge built in the reaction vessel, which makes the device complicated, and the vacuum gauge might be degraded by exposure to plasma.